A printed circuit board (Printed Circuit Board, PCB) is also called a printing circuit board or a printing line board, and is an important integral part for physical support and signal transmission in an electronic product. A futile stub part that is not used for signal transmission in a plated through hole (Plated through hole, PTH) in a PCB board aggravates a signal transmission loss in the PCB, or even impairs integrity of signal transmission. Therefore, a backdrilling manner is commonly used in the industry to minimize a length of the stub part in the PTH, so as to mitigate impact caused by the stub part on the signal transmission of the PCB. It is a key indicator for measuring backdrilling performance to make the length of the futile stub or the distance from an outmost side of the futile stub to a signal layer as short as possible while it is not allowed to drill through the signal layer.
A general practice of backdrilling in the prior art is to preset a backdrilling depth according to different PCBs and different working types, and then perform a backdrilling operation according to the preset depth. Controlling the backdrilling depth is already mature, which is primarily implemented in two manners: One manner is to control a depth by means of pressure sensing, and the other manner is to control a depth by means of electric current sensing. Either of both manners can achieve precision that allows for an error of within 2 mils (a mil is one thousandth of an inch). However, in practical work, due to different processing precision of PCB materials, for a same PCB processing material number, the thickness in the same location of the same type of PCBs of a same batch even varies. That is, a certain thickness tolerance exists. The thickness tolerance is in a proportional relationship with a total thickness of a PCB. A thicker PCB corresponds to a larger thickness tolerance. If backdrilling with a same preset depth is used for a same location of a same type of PCBs, different results are surely to be obtained due to different thicknesses of the PCBs. For a PCB thinner than a standard thickness, the signal layer may be drilled through, and the PCB may become a faulty board; and, for a PCB thicker than the standard thickness, a futile stub that remains after the backdrilling is far larger than a target length, and such a PCB incurs large signal transmission loss while working, or even impairs transmission integrity. Therefore, a primary issue that affects backdrilling precision at present is the PCB thickness deviation, and how to eliminate impact caused by the PCB thickness deviation on backdrilling precision is currently a difficult problem to tackle.